1. Field of the Invention
The present invention relates to a spindle motor and a hard disk drive including the same.
2. Description of the Related Art
Generally, a small spindle motor used in a hard disk drive (HDD) serves to rotate a disk so that a magnetic head is able to write data to the disk or read data written on the disk.
In addition, the spindle motor is provided with a hydrodynamic bearing assembly, and a bearing clearance formed in the hydrodynamic bearing assembly is filled with a lubricating fluid.
In addition, during rotation of a shaft, the lubricating fluid filled in the bearing clearance is pumped to form fluid dynamic pressure, thereby rotatably supporting the shaft.
However, pressure lower than atmospheric pressure, that is, negative pressure, may be generated in the bearing clearance due to the pumping of the lubricating fluid during rotation of the shaft.
In this case, air contained in the lubricating fluid expands, such that air bubbles are formed. When such air bubbles are introduced to a groove pumping the lubricating fluid, deterioration of rotational characteristics such as the generation of insufficient fluid dynamic pressure, the generation of vibrations, and the like, is caused.
Therefore, a circulation hole for decreasing generation of the negative pressure is formed in a sleeve to suppress the generation of the negative pressure.
In the following Related Art Document (US 2009-0080819), a configuration in which a circulation hole for decreasing generation of negative pressure is formed to be inclined and connects a bearing clearance formed by a sleeve and a cover member and a bearing clearance in which a liquid-vapor interface is formed to each other has been used.
However, it is difficult to process the circulation hole and a defect of the sleeve may occur at the time of processing the circulation hole.
In addition, even in the case in which the circulation hole is formed, it may still be difficult to discharge air bubbles contained in the lubricating fluid.